Potassium fertilization of potato in north India Fertilisation potassique de la pomme de terre au nord de l Inde SINGH J.P.

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1 Scientific registration n : 2732 Symposium n : C Presentation : poster Potassium fertilization of potato in north India Fertilisation potassique de la pomme de terre au nord de l Inde SINGH J.P. Central Potato Research Station, Post Bag 1, Jalandhar , India INTRODUCTION Potato is grown in alluvial soils in north India in 0.88 mha as irrigated autumn/winter crop under subtropical short day conditions. This region lies between 27o to 31o N lattitude and 75o to 88o E longitude. The mean tuber yield at farmer s field is 165 q/ha. Unbalanced fertilization heavily in favour of nitrogen is one of the major reasons responsible for low tuber yields. Therefore multilocational replicated trials were done at farmer s field to study the effects of combinations of levels of nitrogen and potassium on tuber yield and quality. MATERIALS AND METHODS Field trials were conducted at 6 locations at farmer s field in Jalandhar district (31o N lattitude and 75o E longitude 237 m above mean sea level). Soil of these locations belong to order Inceptisol classified as Typic Ustochrepts. The soil ph ranged from 6.1 to 7.6, organic carbon ranged from 0.13 to 0.66% (mean 0.32), C.E.C. ranged from 5 to 10 cmol kg-1 (mean 7), available N (Subbiah and Asi ja) ranged from 106 to 282 kg/ha (mean 192), available P (Olsen-P) ranged from 12 to 26 kg/ha (mean16) and available K (ph 7 1N NH4 OAC-K) ranged from 100 to 206 kg/ha (mean 141). The ph of irrigation water ranged from 7.3 to 8.3, electrical conductivity ranged from 0.34 to 0.91 dsm-1 (mean 0.50) and K content ranged from 4.3 to 9.2 ppm (mean 5.6). Treatments comprised of combinations of three levels each of N (80, 160, 240 kg/ha) and K (0, 75 and 150 kg/ha of K2O) along with one control. All the 10 treatments received a common dose of 100 kg/ha of P2O5. Potato tubers of cv. Kufri Jyoti was planted at a spacing of 20 cm in rows 60 cm apart in the first week of October, 1996 and harvested in the last week of January, Plot size was 4.2 x 3.0 m2 each. The crop suffered severe frost 7 weeks to harvest which killed most of the vines. Harvested tuber samples were analysed for quality and weight loss till 4 weeks after harvest. RESULTS AND DISCUSSION Tuber yield Response of tuber yield averaged over 6 locations to 80, 160 and 240 kg/ha of nitrogen (urea) was 56, 76 and 81 q/ha, respectively (Table 1). Similarly the mean response to 75 and 150 kg/ha of K2O (muriate of potash) was 26 and 40 q/ha. Results 1

2 showed that the response to potassium depended on levels o nitrogen. Response to 75 kg/ha of K2O was 11, 38 and 29 q/ha at 80, 160 and 240 kg/ha N, respectively. Corresponding response to 150 kg/ha of K2O was 21, 48 and 49 q/ha. Interaction between N and K was significant. Results showed that for optimum tuber yield potato crop required 160 kg N/ha kg K2O/ha. In Indo-Gangetic plains similar optimum levels of N and K was reported for potato in soils low in available N and K (Singh and Grewal, 1985). Better response to higher levels of K in this study may be attributed to severe frost encountered during the growth period. Potassium imparts resistance to frost injury (Grewal and Singh, 1980). Potassium fertilization significantly increased the yield of marketable large size tubers at the cost of small and medium size tubers (Table 2). Mean increase in yield of large size tubers was 14% with corresponding decrease in the proportion of small and medium size tubers collectively. Increase in total yield and yield of large size tubers may be attributed to the stimulating effect of K+ on photosynthesis, phloem loading and translocation as well as synthesis of high molecular substances within storage organs (Beringer, 1978) contributing to rapid bulking of tubers. Table 1 Effect of levels of nitrogen and potassium on tuber yield of potato (q/ha) in north India Levels of N 2 O 0* Mean Mean L.S.D.(0.05 P) N=7 K=7 NxK=12 * Mean yield in control, not included in means of levels of N and K Table 2 Percentage of different size grade of tubers in the harvested produce as influenced by the levels of n and K fertilization Levels of N Levels of Tuber size 0* Mean K2O 0 L M S L M S L M S L=Large (>75g) ; M=Medium (25-75g) ; S=Small (<25g) * Mean yield in control, not included in means of levels of N and K 2

3 Quality of tubers Increasing levels of N significantly decreased the specific gravity of tubers and tended to decreases the dry matter content of tubers (Table 3). Increasing levels of K significantly decreased the specific gravity and dry matter content of tubers (Table 3). Potassium fertilization tended to increase the vitamin-c content of tubers and decrease the reducing sugars content. However the differences were not significant. Results are supported by the observations of Singh et al, (1995). The N x K interaction effect on quality parameters of tubers was not significant. Table 3 Effect of levels of N and K on quality of tubers at harvest Main effects Dry matter Sp. Gravity Vitamin C Reducing Sugars % (mg/100g tuber) Control Levels of N C.D. (5%) N NS NS NS K NS NS Weight loss from tubers after harvest During four weeks of storage after harvest at room temperature (15-19oC) the weight loss from tubers ranged from 1.48 to 2.09%. Application of 150 kg K2O/ha significantly decreased the weight loss (Table 4). Where as application of nitrogen tended to increase the weight loss. The N x K interaction effect on weight loss was not significant. The role of K+ in osmoregulation in cell saps and in maintenance of ultra structure of cell membranes (Beringer, 1978) might be responsible for reduced weight loss from tubers grown with sufficient potassium fertilization. 3

4 Table 4 Effect of levels of K and K on weight loss (%) from harvest tubers at room temperature storage after harvest Main effects Weight loss (%) Weeks after harvest I II III IV Control Levels of N C.D. (5%) N NS NS NS NS K NS NS NS 0.20 Economics of potassium fertilization Economics of N and K fertilization was worked out by calculating net returns (price of increased yield - additional cost of fertilization). For calculations prevailing whoe sale market price of tubers, fertilizer N and K2O were taken as Rs. 1000/t, Rs. 7.3 and Rs. 6.55, respectively. Net return was maximized by 240 kg N kg K2O)/ha, closely followed by 160 kg N kg K2O/ha (Table 5). All the combinations of N and K fertilization under trial were profitable with benefit : cost ratio (BCR) ranging from 3.2 to 4.7. The mean BCR of N and K fertilization on single nutrient basis was 6.9 and 4.6 respectively. From the results it may be concluded that potassium fertilization along with nitrogen was essential to increase the tuber yield and profitability of potato crop grown in North India. It also improved the nutritive quality of tubers and reduced the weight loss after harvesting. Table 5 Net returns and benefit : cost ratio(bcr) of N and K fertilization to potato Net return (Rs/ha) Levels of N (K 2 O)kg/ha (7.2) 4215 (3.6) 4622 (2.6) (4.7) 7769 (4.6) 7277 (3.2) (3.7) 8524 (3.9) 9031 (3.3) Values in parentheses are BCR 4

5 REFERENCES Beringer, H Functions of potassium in plant metabolism with particular reference to yield. pp In, Potassium in soils and Crops (G.S. Sekhon Ed.). Potash Research Institute of India, New Delhi. Grewal, J.S. and S.N. Singh 1980, Effect of K nutrition on frost damage and yield of potato plants on alluvial soils of the Punjab. Pl. Soil 57: Singh, J.P. and J.S. Grewal Potassium and nitrogen requirements of potato in Indo-Gangetic alluvial plains of varying fertility. J. Potassium Research 1(4): Singh, J.P., R.S. Marwaha dn O.P. Srivastava Processing and nutritive qualities of potato tubers as affected by fertilizer nutrients and sulphur application. J. Indian Potato Assoc. 22: Subbiah, B.V. and G.L. Asi ja A rapid procedure for the estimation of available nitrogen in the soil. Curr. Sci. 25: Keywords: potassium, potato, tuber yield, quality, India Mots clés : potassium, pomme de terre, rendement en tubercules, qualité, Inde 5